This invention relates to a mixing vessel for biochemical treatment of substances with cultures of bacteria, and more particularly to processes such as treatment of wastes, sewage digestion, purification of water and fermentation. The invention relates more particularly to a closed mixing system operable either in a batch or a continuous mode in which turbulent action is induced by injection of partially treated, recirculated waste material and of fluid additives supportive of bacterial-culture growth.
In the past and today in many existing waste treatment plants digestion by aerobic bacteria was and is conducted in large installations in a series of massive holding tanks each having long dwell times and various mixing and aeration devices associated therewith. More recently Venturi aerators have been utilized such as those shown in U.S. Pat. Nos. 3,271,304; 3,334,868 and 3,497,164.
In such prior art apparatuses the arrangement shown do not have the intimate mixing of partially treated waste with aeration fluid prior to and upon injection of the recirculation wastes. The recirculation of the present invention provides active digester operation during required time for digestion and reduces overall time for obtaining effluent purity desired.